Comprehensive Immunophenotypic Profiling and Prognostic Value in Salivary Gland Mucoepidermoid Carcinoma

Objectives: To characterize the proliferative and immunophenotypic profiles of salivary gland mucoepidermoid carcinoma (MEC) and to explore their associations with clinicopathologic features, tumour microenvironment (TME) characteristics, Pan-TRK expression, and disease prognosis. Methods: Forty-one MEC cases were examined using immunohistochemistry for Ki-67, Cytokeratin 19 (CK19), Aquaporin 5 (AQP5), CD3, CD8, and Pan-TRK. Clinicopathologic parameters were correlated with protein expression patterns to assess tumour behaviour and potential TRK fusion activity. Results: Elevated Ki-67 expression correlated with aggressive histologic features and poor clinical outcomes. CK19 expression was significantly reduced in high-grade (HG) MECs, and its loss was associated with unfavourable prognosis. High tumour-infiltrating lymphocyte density correlated with an increased risk, while cases with poor outcomes exhibited heterogeneous CD3⁺ and CD8⁺ T-cell profiles. Pan-TRK expression was detected in only five cases (12.2%), typically weak and heterogeneous, and no robust correlation with cancer recurrence risk was present. Conclusions: The heterogeneous immunophenotypic profiles observed in MEC reflect the biological complexity of the TME. Ki-67 was found to be a reliable indicator of tumour proliferative activity and an unfavourable prognosis. High Ki-67 expression, loss of CK19, and elevated TIL density were associated with increased recurrence risk. Although Pan-TRK expression was infrequent and not prognostically relevant, its occurrence in highly proliferative tumours suggests possible biologic interplay. Expanding immunophenotypic profiling to incorporate spatial analyses and single-cell–level characterization may deepen our understanding of MEC pathogenesis and support personalized therapeutic strategies.